uniform sampler2D backbuffer;
uniform sampler2D channel0;
uniform vec2 channelSize0;
vec2 uv = (gl_FragCoord.xy * 2.0 - resolution.xy) / min(resolution.x, resolution.y);
uv = gl_FragCoord.xy / resolution.xy;
min((resolution.x / resolution.y) / (channelSize0.x / channelSize0.y), 1.0),
min((resolution.y / resolution.x) / (channelSize0.y / channelSize0.x), 1.0)
uv.x * ratio.x + (1.0 - ratio.x) * 0.5,
uv.y * ratio.y + (1.0 - ratio.y) * 0.5
vec3 color = texture2D(channel0, uv).xyz;
gl_FragColor = vec4(color, 1.0);